Typically, a display panel includes a display area and a peripheral area. The display panel includes a plurality of semiconductor elements in the display area. In the manufacturing process of a display panel, the electrical properties of the plurality of semiconductor elements need to be tested to ensure they function properly. To assess electrical properties of the semiconductor elements in the display panel, a pattern of measuring elements, test element group, is formed in the peripheral area of the display panel. The test element group is electrically tested for determining whether semiconductor elements are suitably formed in the display panel.